/ ˈkæləri; NAmE / noun
1.
a unit for measuring how much energy food will produce :
No sugar for me, thanks—I'm counting my calories .
a low-calorie drink / diet
2.
( technical ) a unit for measuring a quantity of heat; the amount of heat needed to raise the temperature of a gram of water by one degree Celsius
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WORD ORIGIN
mid 19th cent.: from French , from Latin calor heat + French suffix -ie (see -y ).